A magnetic disk drive includes a rotating magnetic disk with circular data tracks and read and write heads that may form a merged head which is attached to a slider on an arm that positions the head. During a recording operation, the merged head is suspended over the magnetic disk on an air bearing surface (ABS). The write head has first and second pole pieces that are connected at a back gap region. The first and second pole pieces or yokes have first and second pole tips, respectively, that are separated by a write gap layer and terminate at the ABS. An electric current is passed through coils formed around the back gap region to magnetize the first and second pole pieces. As the leading first pole tip is moved over a magnetic disk, a magnetic flux passes from the second pole tip onto a data track and then to the first pole tip and is called the gap field.
A trend in the industry is to increase the recording density which requires increased coercivity to overcome the demagnetization field of the magnetic transition. However, as the data track width shrinks, the write head field strength tends to decrease due to saturation of the second pole tip region. Unfortunately, a high-end hard disk drive (HDD) generates such a high data rate transfer that not only is greater write head field strength required, but a faster flux rise time is needed. To produce a large enough overwrite value, the write current is boosted and a large overshoot of its waveform results. This condition causes severe excess saturation of the second pole tip and adjacent track erasures often occur.
A conventional planar write head 10 is depicted in FIG. 1 and features a bottom yoke or first pole piece 2 formed on a substrate 1 which may be ceramic, for example. There is a planar top yoke or second pole piece 3 that is connected to the bottom yoke 2 through a back gap region 4 and which is covered by an overcoat layer 14. The bottom yoke 2 has a pedestal 5 with a first pole tip 7 and a throat region 6. The top yoke 3 has a second pole tip region 3a that terminates at a second pole tip 8 at the ABS. The throat region 6 and second pole tip region 3a are separated by a write gap layer 9 which is non-magnetic and extends from the ABS toward the back gap region 4 by a distance TH which is the throat height. At this point, the bottom yoke 2 begins to separate from the top yoke 3 and forms a cavity with sidewalls and a bottom. A conformal first dielectric layer 11 is formed on the sidewalls and bottom of the cavity. A coil layer 13 is wrapped between the top yoke 3 and bottom yoke 2 and around the back gap region 4 and is contained in a second dielectric layer 12 which is coplanar with the top of the write gap layer 9. This design enables the top yoke 3 to be formed on a planar surface to allow good track width control for the second pole tip 8 definition. In a merged head design, the bottom yoke 2 of the write head also serves as the top layer of the read head (not shown).
Referring to FIG. 2, a top-down view of the write head 10 is depicted in which the overcoat layer 14 and dielectric layers 11, 12 have been removed to show the arrangement of the top yoke 3, bottom yoke 2, back gap region 4, and coil layer 13. The top yoke 3 has a length d1 of about 5 to 25 microns which includes the length d2 of the second pole tip region 3a. The maximum width of the top yoke 3 and bottom yoke 2 is w1. The main body of the top yoke 3 behind the second pole tip region 3a is also referred to as the back side region.
Referring to FIG. 3, a side view from the plane 15-15 in FIG. 1 is shown that depicts the second pole tip region 3a and the second pole tip 8 at the ABS end of the top yoke. The write gap layer 9 overlays the first pole tip 7 and the pedestal 5. The second dielectric layer 12 is on either side of the write gap layer 9 and pedestal 5 at the ABS while the second pole tip region 3a is surrounded on the top and sides by the overcoat layer 14.
In a conventional planar writer shown in FIG. 4 which is an enlarged view of the ABS end of write head 10 in FIG. 1, the top yoke 3 can provide a significant amount of flux 16 toward the write gap layer 9. The flux 16 passes from the second pole tip region 3a through the second pole tip 8 onto a recording track (not shown) and then through the first pole tip 7 and into pedestal 5. However, there is some leakage represented by a flank field 17 across the ABS onto an adjacent recording track. When a high write current is employed with large overshoot waveforms, then a significant amount of erasure on adjacent data tracks occurs because of the flank field. Therefore, a new write head design is needed that reduces the flank field to prevent unwanted data track erasure.
In U.S. Pat. No. 6,473,276, a merged magnetic head which includes a write head with a single sided notched first pole piece is described. A data track is formed that has a narrow erase band on one side and a wide erase band on the other side. The narrow erase band enables a large signal amplitude while a wide erase band allows flexibility in spacing the read head from adjacent tracks.
A magnetic write head with a zero throat height (ZTH) layer is disclosed in U.S. Pat. No. 6,111,724. The ZTH is formed close to the first and second pole tips to reduce flux loss between the first and second pole pieces. The method of forming the ZTH layer avoids reflective notching and thereby improves definition of the second pole tip.
Another second pole piece is described in U.S. Pat. No. 6,337,783 where a second yoke component is stitched to the back and sides of the top edge of a second pole tip to provide improved magnetic coupling. The top stitched area is minimized so that the coil layers may be closer to the ABS to increase the data rate of the head. In related art disclosed in U.S. Pat. No. 6,029,339, the stitching of the yoke component to the second pole tip is achieved by a method that avoids reflective notching in the top yoke.
Unwanted side writing is prevented in U.S. Pat. No. 6,504,675 by modifying the second pole tip such that the leading edge of the pole tip is narrower than the trailing edge. Thus, the second pole tip has a trapezoidal cross-section with tapered sides.